The present invention relates to a blind fastener such as a blind nut or a blind rivet, and to a heat treatment method therefor. More specifically, the present invention relates to the sleeve of a blind fastener and a heat treatment method therefor able to harden the surface and increase the elongation of the hollow sleeve of a blind fastener.
A blind fastener such as a blind nut or a blind rivet has a hollow sleeve with a flange on one end. The sleeve is inserted into a mounting hole in a fastened component such as a panel or another part, and the hollow portion of the sleeve is partially expanded in the outward direction radially so as to interpose the fastened component such as a panel or another part between the expanded portion of the sleeve and the flange of the sleeve. In this way, the fastened component can be securely fastened. When one of the fastened components is a panel and the other fastened component is a part, the part is secured to the panel using a blind fastener. The use of a blind fastener is advantageous because it can be fastened using a blind operation from only one side of the fastened component, even when the fastened component has a wide area such as an automotive panel. The characteristics required of a blind fastener include a hard sleeve in order to obtain high fastening strength, and sufficient elongation when the sleeve is expanded. If the sleeve of the blind fastener does not have sufficient hardness and sufficient elongation, it cannot obtain high fastening strength and may crack when expanded and deformed. In either case, adequate fastening cannot be performed.